Generally, the speed of an integrated microprocessor circuit can be limited by the speed of electrical signal propagation through the BEOL (back-end-of-the-line) interconnects. Ultralow k (ULK) dielectric materials having a dielectric constant of about 3.2 or less permit a BEOL interconnect structure to transmit electrical signals faster, with lower power loss, and with less cross-talk between metal conductors such as, for example, Cu. Porous materials typically have a dielectric constant that is less than the non-porous version of the same material. Typically, porous materials are useful for a range of applications including, for example, as an interlevel or intralevel dielectric of an interconnect structure.
A typical porous dielectric material is comprised of a first solid phase and a second phase comprising voids or pores. The terms “voids” and “pores” are used interchangeably in the present application. A common aspect of porous materials is the problem of controlling the characteristic dimensions of the pores and the pore size distribution (PSD). The size and PSD have strong effects on the properties of the material. Specific properties that may be affected by the pores size or the PSD of a dielectric material include, for example, electrical, chemical, structural and optical. Also, the processing steps used in fabricating the BEOL interconnect structure can degrade the properties of an ULK dielectric, and the amount of degradation is dependant on the size of the pores in the ULK dielectric. The foregoing may be referred to as “processing damage”. The presence of large pores (larger than the maximum in the pore size distribution) leads to excessive processing damage because plasma species, water, and processing chemicals can move easily through large pores and can become trapped in the pores.
Typically, the pores in an ULK dielectric have an average size (i.e., majority of the pores) and also have a component of the PSD that is comprised of larger pores (on the order of a few nm) with a broad distribution of larger sizes due to pore connection as the pore density increases (i.e., minority population of larger pores).
The minority population of larger pores allows both liquid and gas phase chemicals to penetrate into the ULK film more rapidly. These chemicals are found in both wet and plasma treatments that are routinely used during integration of the ULK dielectric material to build an interconnect structure.
The above-mentioned problems are not specific to porous dielectric materials. Instead, they are generally present in non-dielectric materials including, for example, semiconducting, ceramic and metal.
In view of the above, there is a need for providing composite materials in which all the pores within the composite material are small having a diameter of about 5 nm or less and with a narrow PSD. There is also need for providing a method of fabricating composite materials in which the broad distribution of larger sized pores is substantially eliminated from the material.